Heavy media separation process



Dec. 13, 1955 F. J. FONTEIN 2,726,764

HEAVY MEDIA SEPARATION PROCESS Filed Sept. 9, 1952 2 Sheets-Sheet 1 g 2I I Dec. 13, 1955 F. J. FONTEIN 2,725,764

HEAVY MEDIA SEPARATION PROCESS Filed Sept. 9, 1952 2 Sheets-Sheet 2 1 III7 2/ United States atent O HEAVY MEDIA SEPARATION PROCESS Freer-k 3.Fontein, Heerlen, Netherlands, assignor to Stamicarhon N. V., Heerlen,Netherlands Application September 9, 1952, Serial No. 308,654

Claims priority, application Netherlands September 24, 1951 1 Claim.(Cl. 209-1725) This invention relates to the separation of heterogeneousmixtures of small solid particles having difierent specific gravities bymeans of a separating suspension of fine magnetic particles in a liquid.In such processes two fractions are obtained, one consisting ofseparating suspension-also called heavy mediumand the specifically lightparticles of the mixture and the other consisting of heavy medium andthe specifically heavy particles of the mixture. In both fractions theparticles of the mixtures are then separated from the heavy medium. Thusthe heavy medium is recovered and can be used again.

If the particles of the mixture are larger than about 1 mm. the mediumcan easily be recovered by screening of the separated fractions. If theore contains smaller particles, however, screening of those particles isnot efficient since fine screening is an expensive operation. With finesolid particles therefore the magnetic particles of the medium arerecovered by means of magnetic separators. That procedure also hasdisadvantages: magnetic separators are expensive and a small portion ofthe magnetic particles always gets lost therein.

Now it is the main object of this invention to provide a heavy mediaseparation process for separating mixtures of solid particles whereinheavy medium is recovered tom the separated fractions without the use ofscreens being necessary and wherein a substantial portion of at leastone separated fraction is not passed through a magnetic separator. Morein particular it is the object of this invention to provide such aprocess for separating ores which substantially only contain particlesranging in size down to 0.1 mm.

Since in general the best separating results are obtained when stableseparating suspensions are employed it is a further object of thisinvention to provide a process of this kind in which use can be made ofa stable suspension.

In summary, the above, and possibly other objects are attained in aprocess comprising the following steps. A liquid mass is formedconsisting on the one hand of the mixture of solid particles to beseparated, at least 95% by weight of which should be larger than 80microns and on the other hand of a liquid separating suspension ofmagnetically susceptible particles, for instance magnetite orferrosilicon particles, which for at least 85% by weight should besmaller than 60 microns and preferably fine enough to form asubstantially stable suspension, said separating suspension having asignificantly lower specific gravity than the particles of the mixture.This liquid mass is then separated into two fractions, one of whichcontains separating suspension and the bulk of the specifically heavierparticles of the mixture, the other containing separating suspension andthe bulk of the lighter particles of the mixture. Such a separation canfor instance be effected in a jig or in a hydrocyclone of the kinddescribed in the co-pending applcation Serial No. 228,834 filed on May29, 1951 in the name of Fontein and Dijksman and now abandoned. The nextstep consists of classification of the fraction of specifically lighterparticles and separating suspension. For this purpose preferably use ismade of a hydrocyclone classifier such as for instance has beendescribed in British Patent Specification 651,094. The cut is made suchthat the bulk of the specifically lighter particles of microns and moregoes into the coarser classified fraction and that the bulk of themagnetically susceptible particles goes into the finer classifiedfraction. To this end the magnetically suscepticle particles are verysmall, and preferably the separating suspension should be substantiallystable. As the separating suspension has a significantly lower specificgravity than the specifically lighter particles of the mixture theseparticles can settle in the suspension, which makes the classificationstep possible.

The finer classified fraction is returned to the process to be used forforming a liquid mass with further mixed solid particles to beseparated. The coarser classified fraction is subjected to magneticseparation.

If the mixture to be separated contains particles which are smaller than80 microns the finer classified fraction contains a large portion ofthose fine particles. As this fraction is recycled the fine particlestend to accumulate to a certain extent, but since the amount of fines inthe mixture to be separated is only small, this accumulationsubstantially does not affect the process. In operation equilibrium willestablish so that the amount of fines introduced into the system is thesame as the amount of fines removed therefrom by the magneticseparators. Thus the measure of accumulation depends on the ratio of thevolumes of the two classified fractions. If the coarser fraction has arelatively large volume there is little accumulation, but then also arelatively large portion of the separating suspension will go into thecoarser classified fraction. Since it is desired to get the largestpossible amount of separating suspension in the fine classified fractiona relatively high measure of accumulation of lines should be allowed,but of course the concentration of fines should not be allowed toincrease too far, for instance not above 400 grams per liter. It thuswill be clear that, to obtain the highest efiiciency, supervision of theprocess may be necessarylso as to attune it to possible changes of thecomposition of the feed.

In order that the invention may be the more readily understood,reference is hereinafter made to the accompanying diagrams, in which, byway of example, Fig. 1 represents a longitudinal section of ahydrocyclone specific gravity separator, suitable for use in theprocess, Fig. 2 being a section at right angles to the axis of thehydrocyclone shown in Fig. 1 and Fig. 3 is a diagram of an ore-dressingplant according to the invention.

Referring to Figs. 1 and 2 of the drawing, 1 is the feed conduit of thehydrocyclone, which conduit leads tangentially into a cylindrical part 2of the cyclone chamber which has a smooth interior surface and comprisesthe said cylindrical part conjoined to a conical part 3. The apexdischarge aperture of the hydrocyclone is designated 4, the cover-plate6, and 5 designates a pipe passing through the cover-plate, which pipeforms the vortex finder which extends axially into the hydrocyclonechamber and also defines the overflow aperture of the hydrocyclone.

Referring now to the plant diagrammatically represented in Fig. 3, themixture to be separated a, a substantially stable magnetite suspensionb, and recycled magnetite suspension are mixed in a vessel '7 with thehelp of an agitator 8 actuated by a motor 9. The pump 10 supplies thismixture continuously from the tank 7 to a battery of hydrocyclonewashers 11 connected for operation in parallel. Only one cyclone of thebattery is shown. Said hydrocyclones 11 are of the type described in theaforesaid co-pending patent application 228,834 their dimensions beingsuch as to ensure that the specific The fraction leaving thehydrocyclones 11 through the discharge apertures 4 (the apex fraction)comprises substantially all particles of the mixture to be separatedwith a specific gravity higher than the specific gravity of separation,and has a higher percentage content of solid' matter, whereas thefraction leaving the hydrocyclones through the overflow apertures (theoverflow fraction) consists mainly of particles specifically lighterthan the said specific gravity of separation.

The apex fraction of the hydrocyclonesll is collected in an open toppedvessel 12, and after being diluted with water it is passed to themagnetic separators 13 and 14, which have been so arranged in series,that the nonmagnetic fraction from 13 is subjected to an after-treatmentin 14. The non-magnetic fraction d from the magnetic separator 14comprises substantially 'all particles of the mixture to be separatedhaving a specific gravity higher than the specific gravity ofseparation. Subsequently, the water may be recovered from this fractionand resupplied to the process.

The overflow .fraction from the hydrocyclone 11' is collected in theopen topped vessel 15 and is subsequently continuously and underpressure, by means of pump 16, supplied to a battery of hydrocycloneclassifiers 17, connected to operate in parallel, (Only oneof thehydrocyclones 17 is shown.) The dimensions of the hydrocyclone 17 aresuch, that the overflow fraction from the hydrocyclones 11 is separatedinto a concentrated apex fraction comprising substantially all theparticles of the mixture to be separated which are fed into thehydrocyclones 17, and an overflow fraction mainly consisting ofseparating suspension. This overflow fraction is collected in the opentopped vessel'21 and is subsequently returned to vessel 7. q

The apex discharge from the hydrocyclones 17 is collected in theopen'topped vessel 18 and, after being diluted with water, is passed tothe magnetic separators 19 and 20 which have been so arranged in series,that the non-magnetic fraction from 19 is subjected to an after.-treatment in 20. The non-magnetic fraction e from the magnetic separator20 consists almost exclusively of particles of the mixture to beseparated having a specific gravi'ty' lower than the specific gravity ofseparation. Subsequently, the water may be recovered from this fractionand resupplied to the process. The magnetic fractions from the magneticseparators 13, 14, 19 and 20 are thickened in a thickener 22. Theoverflow fraction from the thickener 22 is returned to the magneticseparators 13 and 19 by the pump 23, the thickened magnetite suspensionbeing returned to the vessel 7.

'Any magnetite goingto waste with the fractions d and V e is made up forby supplying fresh magnetite to the vessel 7. 'The concentration of theseparating suspension is controlled in a known manner.

The system of Fig. 3 is particularly suited for separating mixtures ofparticles which substantially are larger than 80 microns and smallerthan 4 mm. A Washing circuit for coarser particles can of course beconnected in parallel to the system of Fig. 3, and in that case it is ofadvantage to have a single circuit of'the separating suspensions for thetwo Washing circuits. Thus it is possible to feed diluted suspensionfrom the washing circuit for coarser particles to thickener 22 and touse part of the clarified Water from thickener 22 and separatingsuspension from vessel 7 in the circuit for coarser particles.

Example An'installation as shown in Fig. 3 is used for concentrating the0.5-4 mm. fraction of a galenite ore. The specific gravity of the ganguewas 2. 6. The lead content was 4.02%

'For treating 26 tons per hour use was made of 15 hy drocyclone-washers'11 arranged in parallel and 12 hy- Specific Quang a gg g Lead gravitytity, ore grams] content, magnetite m3 iiter .percent sussiggn- Feed tothe hydrocyclone washers '134 202 3. 85 2. 1 Apex fraction fromthehydrocyclone washers 4 1300 18. 6 2. 4 Overflow fraction from the 1 Vhydrocyclone washers 130 167 0. 17 7 2. 095 Feed to the hydrocycloneclassifiers 130 167 0. l7 2. 095 Apex fraction from the hydrocycloneclassifiers 22 935 0. 17 2. 2 Overflow fraction from the t hydrocycloneclassifiers. 108 e 10 0. 15 2. O8

drocyclone classifiers 17 likewise arranged in parallel,

their dimensions being as follows:

Hydrocy- Hydrocyt. clone washers g i Internal diameter cycliudrical part2 Height cylindrical part 2 Apex angle conical part 3. Inside diameterteed pipe 1 Inside diameter vortex finder 5 Length of vortex finder 5within the hydrocyclone 48mm. 7 48 mm.

Diameter apexaperture4 24rmn 2 4mm. Feedpressurenn, 1 at. gauge 1 at.gauge a pressure. pressure.

The separating suspension consisted of magnetite Under these conditions,the feed to the hydrocyclone washers consequently contains about 169tons of magnetite per hour, 144 tons per hour being immediately recycledtogether with the overflow fraction from the hydrocylone classifiers,only 25 tons of magnetite per hour oeing recoverable by the magneticseparators; From this it is clear, that the invention makes it possible,to

reduce the quantity of magnetite requiring to be mag-g neticallyrecovered and to considerably reduce Lille mag netite losses.

1 claim:

in a process of separating according to specific gravity a mixture ofsolid particles which for at least.9 5 by weight are larger than micronsthe combination of steps which comprises: forming a liquid massof saidmixture with a liquid separating suspension of magneti cally susceptibleparticles which .for at least .by. weight are smaller than 60 microns,said suspensionhaving a significantly lower specific gravity than theparticles of the mixture; separating said liquid mass into two fractionsone of which contains separating suspension and the. bulk of thespecifically heavier particles of the mixture, the other containingseparating suspension and the bulk.

of the specificallylighter particles of the mixture; classifying thefraction of specifically lighter particles and separating suspension,making the cut such that the, bulkof the magnetically susceptibleparticles goes into the finer classified fraction and that a majorportion of the specifi- V cally lighter particles of the mixture goesinto the coarser classified fraction; returning the finer classifiedfraction for forming a liquid mass with further mixed solid par-.-ticles and subjecting the coarser classified fraction .to mag neticseparation. v p

References Cited i the file of this patent FOREIGN PATENTS GreatBritain' Aprl 4, 1951

